Puberty is a Critical Period for Vomeronasal Organ Mediation of Socio-sexual Behavior in Mice

Genetic disruption of the vomeronasal organ (VNO), an organ responsible for pheromone processing, drastically alters socio-sexual behavior in mice. However, it is not known whether the VNO has a role during the pubertal organizational period when sex-typical socio-sexual behaviors emerge, or if disruption of the organ in adulthood is sufficient to alter socio-sexual behavior. To bypass the lifelong VNO disruption of genetic knockout models, we surgically ablated the VNO of male and female mice either during the peripubertal period [postnatal day (PND) 28–30] or adulthood (PND 58–60), with sham controls at both ages. We ruled out anosmia via the buried food test and assessed sexual odor preferences by simultaneously exposing mice to same- and opposite-sex soiled-bedding. We then measured territorial aggression with the resident-intruder paradigm and assessed sexual behavior in response to an encounter with an estrus-induced female. Neural activity approximated by FOS-immunoreactivity along the VNO-accessory olfactory pathway was measured in response to opposite-sex odors. We found that peripubertal VNO ablation decreased sexual odor preferences and neural activity in response to opposite-sex odors, and drastically reduced territorial aggression in male mice. Conversely, adult VNO ablation resulted in subtle differences in sexual odor preferences compared with sham controls. Regardless of the VNO condition, mice displayed sex-typical copulatory behaviors. Together, these results suggest that puberty is a critical period in development whereby the VNO contributes to the sexual differentiation of behavior and neural response to conspecific odors.

Odor-Mediated Group Organization and Coordination in the Termite-Raiding Ant Megaponera analis (Mayr)

Visual and olfactory communications are vital for coordinated group hunting in most animals. To hunt for prey, the group-raiding termite specialist ant Megaponera analis, which lacks good vision, must first confirm the presence or absence of conspecific raiders. Here, we show that M. analis uses olfactory cues for intraspecific communication and showed greater preference for conspecific odors over clean air (blank) or odors from its termite prey. Chemical analysis of ant volatiles identified predominantly short-chained hydrocarbons. Electrophysiological analysis revealed differential sensory detection of the odor compounds, which were confirmed in behavioral olfactometric choice assays with odor bouquets collected from major and minor castes and the 2 most dominant volatiles and n-undecane n-tridecane. A comparative analysis of the cuticular hydrocarbon profile with those of the short-chained odor bouquet of different populations shows a high divergence in the long-chained profile and a much-conserved short-chained odor bouquet. This suggests that there is less selection pressure for divergence and individual recognition in the short- than the long-chained odor profiles. We conclude that olfactory communication serves as an alternative to visual or sound communication, especially during group raids in M. analis when ants are not in direct contact with one another.

Behavioral Responses to 'Alarm Odors' In Potentially Invasive and Non-invasive Crayfish Species from Aquaculture Ponds

Two North American crayfish species, the Eastern white river crayfish, Procambarus acutus acutus, and the red swamp crayfish, P. clarkii, were studied in the laboratory for their responses to food odors and to cues released by injured conspecifics and heterospecifics. The two species differ in that only P. clarkii is known to behave as an invasive species. All the test individuals were collected from aquaculture research ponds, in which they had had no prior contact with the other species and predation risks, excluding cannibalism, were reduced. The experimental design consisted in subjecting 20 crayfish per species to (1) a 3-min control phase after the injection of 20 ml of water and (2) a 3-min test phase after the injection of 20 ml of one of three test solutions (food odor, conspecific odor plus food odor, heterospecific odor plus food odor). We found that the two species differ on one hand for their background behavior and on the other for the intensity and quality of their responses to the three types of cues. Firstly, P. clarkii appeared more active than P. acutus acutus during the control phase and responded in a stronger fashion to the injection of the solutions. Secondly, we recorded an increased locomotion in P. acutus acutus with food and heterospecific cues (by moving crayfish maximize the chance of finding food), but not with conspecific odors (by not moving, crayfish reduce their exposure to visual predators). To the contrary, at the injection of the three test solutions P. clarkii displayed clear feeding-related activities (although less intense with conspecific odors) as opposed to the danger reactions shown in a previous study on individuals from a naturalized population of the same species. This result suggests that crayfish reared in an environment where predation risks are reduced (e. g. in aquaculture ponds) may respond differently to cues that in other, more risky habitats inform of a danger.